Cerrejón Formation

The Cerrejón Formation is a geologic formation in Colombia dating back to the Middle-Late Paleocene. It is found in the El Cerrejón sub-basin of the Cesar-Ranchería Basin of La Guajira and Cesar. The formation consists of bituminous coal fields that are an important economic resource. Coal from the Cerrejón Formation is mined extensively from the Cerrejón open-pit coal mine, one of the largest in the world. The formation also bears fossils that are the earliest record of Neotropical rainforests. The formation was first named Septarias Formation and in 1958 renamed to Cerrejón Formation by Thomas van der Hammen, probably based on an earlier report by Notestein. Cesar-Ranchería Basin The Cerrejón Formation, with an assigned total thickness of , is subdivided into lower, middle, and upper groups based on the thickness and distribution of coal beds. On average the coal beds are thick, and range from to in thickness. The thickest beds are in the upper part of the formation. The Cerrejón Formation is laterally equivalent with the Los Cuervos and Bogotá Formations to the south; Llanos Orientales and Altiplano Cundiboyacense respectively. The formation is also time-equivalent with the Marcelina Formation of the Venezuelan Serranía del Perijá and the Catatumbo Formation of the southwestern Colombian part of the Maracaibo Basin, the Catatumbo Basin. The formation has also been described as laterally equivalent to the Mostrencos and Santa Cruz Formations of Venezuela. Based on lithofacies associations and paleofloral composition, the depositional environment fluctuated from an estuarine-influenced coastal plain at the base of the formation to a fluvial-influenced coastal plain at the top. In the geologically recent past, some coal in the formation has spontaneously and naturally combusted to form clinker, red and brick-looking burnt coal. These rocks outcrop irregularly and are up to thick. Clinker is found near deformed zones such as faults or tight folds, and is older than the deformities themselves.